The present invention relates to a new pin box assembly for a trailer that provides both softening in the vertical direction and anti-chucking in the longitudinal or horizontal direction so as to provide enhanced performance and a smoother ride. In effect the pin box assembly acts as a buffer between the tow vehicle and the trailer, significantly reducing the negative impact of vertical shock and longitudinal chucking to provide an improved ride. The assembly relieves stress on the towing vehicle, trailer frame, cabinets, mechanicals and support mechanisms. The smoother ride also reduces fatigue for drivers and passengers in the towing vehicle.